module _79

open System.IO

let findPasscode =
    let logins = 
        File.ReadAllLines(@"79_keylog.txt") 
    let preceeds = 
        logins 
        |> Seq.collect (fun login -> seq { yield (login.[0], login.[1]); yield (login.[1], login.[2]) })
        |> Seq.distinct

    let collectTuple (a,b) =
        seq { yield a; yield b }

    // topographical sort kinda
    let rec orderGraph g =
        seq {
            if Seq.length g = 1 then 
                yield (collectTuple (Seq.nth 0 g)) |> Seq.toList
            else
                let allNodes = g |> Seq.collect collectTuple |> Seq.distinct |> Set.ofSeq
                let sndNodes = g |> Seq.map snd |> Seq.distinct |> Set.ofSeq
                let noPreceedingNodes = allNodes - sndNodes
                for n in noPreceedingNodes do
                    let gMinusN = g |> Seq.filter (fun gi -> not(fst gi = n))
                    for s in orderGraph gMinusN do
                        yield n :: s
        }
    
    preceeds
    |> orderGraph
    |> Seq.toArray